It is known that cathodes, phosphorescence screens, and luminescent devices degrade during work in vacuum, and their life expectancy depends on the accumulated time of active work, as well as on the number of ON and OFF switchings. With the lapse of the accumulated operation time performance characteristics of the aforementioned devices are worsened, and therefore these devices can be used to a predetermined limit.
For the night vision optical devices, such as night vision riflescopes with image intensifiers, in addition to the accumulated time of active work, the life expectation of the scope also depends on the number of so-called muzzle flashes, which occur during nighttime shooting. In fact, the accumulated number of flashes of bright light is one important criterion that determines the service life of the sight with the night-vision optics.
Attempts have been made to extend the service life, e.g., of night vision devices with image intensifying tubes by utilizing an adjustable variable gain. Thus U.S. Pat. No. 6,150,650 issued in 2000 to J. Bowen, et al. describes a night vision device which utilizes an image intensifier tube, wherein the image intensifier tube has a given life expectancy, the image intensifier tube being subjected to factory calibration for providing an optimum output during operation, wherein the calibration undesirably differs from tube to tube and is adjustable by variable control means coupled to the tube, whereby when one tube is substituted for another the difference in calibration causes non-optimum performance. The method includes the steps of: determining minimum and maximum gain limits associated with the optimum output of the night vision device; factory calibrating gain limiting means according to the determined minimum and maximum gain limits, wherein the gain limiting means are associated with the image intensifier tube and for limiting the variable control means; and, tethering the gain limiting means to the image intensifier tube.
In other words, since the gain of an image intensifier tubes supplied by the manufacturers and used in firearm aiming device changes, it is proposed to adjust the gain with reference to the changes in order to maintain the gain at a relatively constant level. This is because some of the factory-supplied image intensifier tubes are overadjusted to an excessive gain or power and will have a shortened life time, while others are underadjusted and though will have a longer service life, will not work with a required efficiency. This means that variations in the life expectancy of the image intensifiers may occur in a very broad range. The optimization proposed in U.S. Pat. No. 6,150,650 narrows the above range. It Is understood, however, that in order to efficiently control the workability of the night vision optics, it is important to known the expected service life of the night vision optics in order to replace it in time. This is especially important for night-vision optics used in night-vision sights of a firearm, where unexpected failure of the sight under combat conditions is absolutely Intolerable.
It is understood that in reality the life expectancy of a night vision optics may vary in a very wide range depending on specific conditions of practical application. For example, when a night vision optics is used in an optical aiming device of a firearm that contains an image intensifier and when it is used in intensive battle conditions with frequent muzzle flashes which shorten the lifetime of the image intensifier because of a high light load, the life time of such an aiming device will be shorter than in the case of a sniper work who keeps the night vision optics in the ON condition over a long time but without flashes and under a low light load. In other words, the life expectation of la night vision device with cathodes, fluorescent screens, and similar items operating in vacuum will depends, among other things, on two main factors: the accumulated time of actual operation (SWITCHED-ON condition) of the night vision optics and the number of muzzle flashes when the optics operates with a very high light load.
As far as a firearm is concerned, It is understood that with the lapse of time any weapon loses Its initial performance characteristics. Although the weapon is subject to damages caused by natural causes such as corrosion, loosening of fasteners, creeping and ageing deformation of the materials, or the like, these changes are normally revealed after such long period of time when the weapon becomes practically obsolete and is replaced by several new generations. On the other hand, when the weapon is frequently used for its direct purpose, i.e., for shooting, the process of weapon degradation is accelerated with a factor of several thousand. This is because shooting is accompanied by friction and wear, e.g., on the inner surface of the weapon barrel. Therefore, attempts have been made to limits the service life of a weapon by counting the number of shots. For example, U.S. Pat. No. 5,918,304 issued in 1999 to Karl Gartz describes an apparatus for monitoring the firing stress of a weapon barrel. It is stated that the barrels of particularly large-caliber weapons have to be replaced for safety reasons after firing a predetermined number of rounds. For this purpose a “barrel log” must be maintained in which the number of rounds fired from the barrel and the respective charge type (if different charges are used for the barrel) have to be entered. The invention is essentially based on the principle to measure, with a suitable sensor, the actual body sound signals (body oscillations) obtained upon the firing of the weapon and to compare the signals in an electronic evaluating apparatus with reference signals which characterize the different charges and which are stored in a memory. The charge value which is associated with the actual signal value and which is obtained from such a comparison is subsequently stored in a non-volatile memory of the evaluating apparatus and is added to an already stored charge value. The same applies to the number of shots measured by the sensor. The accumulated firing stress may be automatically and very accurately determined and may be at any time retrieved from the memory (electronic barrel log). Further, the apparatus may serve as a counter of fired rounds. Also, the apparatus may be utilized for determining the barrel condition because a change of the barrel condition leads to a characteristic change of the frequency spectrum of the measuring signal.
For the modern weapon, which is equipped with various optical and electronic devices, this problem is especially aggravated, but the weapons which are most of all sensitive to impacts resulting from the shots and recoil forces are those which are equipped with electro-vacuum devices such as image intensifiers, some distance ranges, night-vision optics, etc. In other words, for firearms used in combination with night-vision optics or similar devices that utilize vacuum electronic units with cathodes, phosphorescence screens or the like, the life expectation of the firearm is determined not only by the number of shots, wear, or mechanical damage but also by the service life of the aforementioned optical devices which is normally limited to several thousand hours of active work and, as has been mentioned above, to a great extent depends on the number of muzzle flashes acting-on cathodes, phosphorescence screens, luminescent devices, or similar elements of vacuum night vision optics.
However, none of the existing prior-art devices known to the applicant are used for controlling or diagnosing the life expectation of the night vision instruments with reference to three aforementioned factors (number of shots, active time of operation of the night vision optics, and number of muzzle flashes during the use of the night vision optics) and their relationship.